Differential locking mechanism

ABSTRACT

In a differential locking mechanism, a first differential side gear is fixed on a first axle, a second differential side gear is fixed on a second axle, and a bull gear including an engagement part is disposed between the first and second side gears. A cylindrical part is provided on the first differential side gear unrotatably relative to the first differential side gear, and includes a circumferential portion surrounding the first differential side gear. A differential locking slider is fitted on the circumferential portion of the cylindrical part unrotatably relative to the cylindrical part and axially slidably. The differential locking slider is slidable in a direction to engage its engagement part with the engagement part of the bull gear, and in another direction to disengage its engagement part from the engagement part of the bull gear.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority under 35 U.S.C.§119(e) based on U.S. Provisional Application Ser. No. 62/314,767 filedon Mar. 29, 2016, the entire content of which is also incorporatedherein by reference.

FIELD

At least one embodiment of the present invention relates to adifferential locking mechanism, especially, for a differential gear unitin a transaxle.

BACKGROUND

As disclosed by U.S. Pat. No. 6,007,449 A, there is a well-knownconventional transaxle. This transaxle includes a transaxle casingincorporating a hydrostatic transmission (“HST”), a differential gearunit, right and left axles differentially rotatably connected to eachother by the differential gear unit, and a reduction gear train fortransmitting power from the HST to the differential gear unit. When theinterior of the transaxle casing is viewed in plan, the right and leftaxles are extended rightward and leftward distally from the differentialgear unit, the reduction gear train is extended from the differentialgear unit perpendicular to the axial direction of the axles, and the HSTis disposed in a substantially rectangular HST chamber. If the reductiongear train is assumed to extend forward from the differential gear unit,the reduction gear train defines a left side of the HST chamber, and theright axle defines a rear side of the HST chamber. Therefore, a cornerof the HST chamber between the left side and the rear side is adjacentto the differential gear unit.

The differential gear unit constitutes a conventional differentiallocking mechanism including a thrust collar and a shifter. The thrustcollar is fitted on one of the right and left axles so as to beunmovable axially along the axle. The shifter is fitted on the thrustcollar slidably along the thrust collar in the axial direction of theaxle. Locking pins are extended from the shifter parallel to the axle soas to constantly pierce a differential side gear fixed on the axle. Thelocking pins are further inserted into respective recesses formed in abull gear of the differential gear unit so as to lock the right and leftaxles to each other via the bull gear only when the shifter slides alongthe thrust collar toward the differential side gear for the purpose ofdifferential locking of the axles. Normally, the shifter is located soas not to insert the locking pins into the recess formed in the bullgear, thereby allowing the right and left axles to rotatedifferentially.

In the conventional differential locking mechanism, the thrust collarand the shifter are disposed on a distal side of the differential sidegear in the axial direction of the axle. In this regard, the abovedisclosed transaxle is comparatively large-sized, so that the rear sideof the HST chamber is spaced forward from the right axle. Therefore, thespace between the rear side of the HST chamber and the right axle isused for locating the thrust collar and the shifter, so that the thrustcollar with the shifter thereon is provided on the right axle. However,if the transaxle is small-sized, there may be no space between the rearside of the HST chamber and the right axle for locating the thrustcollar and the shifter. Further, if the thrust collar with the shifterthereon is provided on the left axle, a portion of the transaxle casingsupporting the left axle on the leftward distal side of a differentialside gear on the left axle may have to be modified to expand leftward toincorporate the thrust collar and the shifter, thereby conflicting withthe demand for minimizing the transaxle, and thereby increasing costs.Therefore, to ensure a small-sized transaxle, it is desired that adifferential locking mechanism is minimized, especially, in an axialdirection of axles.

SUMMARY

A differential locking mechanism according to an embodiment is minimizedfor realizing a small-sized apparatus, e.g., a transaxle, incorporatinga differential gear unit constituting the differential lockingmechanism.

A differential locking mechanism according to the embodiment comprisesfirst and second axles, first and second differential side gears, a bullgear, a differential pinion, a cylindrical part, and a differentiallocking slider. The first and second axles are extended coaxially toeach other. The first differential side gear is fixed on the first axle.The second differential side gear is fixed on the second axle. The bullgear is disposed between the first and second side gears. The bull gearincludes an axial center hole and an engagement part radially outwardfrom the axial center hole. Axial proximal ends of the first and secondaxles are fitted in the axial center hole so as to face each other sothat the first and second axles are rotatable relative to each other andto the bull gear. The differential pinion is pivoted in the bull gearand meshes at opposite sides thereof with the first and seconddifferential side gears. The cylindrical part is provided on the firstdifferential side gear unrotatably relative to the first differentialside gear. The cylindrical part includes a circumferential portionsurrounding the first differential side gear. The differential lockingslider is fitted on the circumferential portion of the cylindrical partunrotatably relative to the cylindrical part. The differential lockingslider includes an engagement part. The differential locking slider isslidable along the circumferential portion of the cylindrical part inone axial direction of the first and second axles so as to engage theengagement part of the differential locking slider with the engagementpart of the bull gear, and in another axial direction of the first andsecond axles so as to disengage the engagement part of the differentiallocking slider from the engagement part of the bull gear.

Therefore, the cylindrical part and the differential locking slider arenot located on a distal side of the first differential side gear in theaxial direction of the first and second axles, but are located radiallyoutward from the first differential side gear so as to surround thefirst differential side gear. Therefore, the differential lockingmechanism is advantageously minimized in the axial direction of thefirst and second axles. In a case where the transaxle, having theabove-mentioned arrangement of the HST, the reduction gear train, theaxles and the differential gear unit, is provided with the presentdifferential locking mechanism, the transaxle does not need expansion ofthe transaxle casing. More specifically, if the first axle having thefirst differential side gear thereon is the right axle of theabove-mentioned transaxle, the HST can be disposed extremely adjacent tothe right axle with no space along the right axle on the distalrightward side of the right differential side gear for arranging thethrust collar and the shifter, thereby achieving the desired small-sizedtransaxle. If the first axle having the first differential side gearthereon is the left axle of the above-mentioned transaxle, the portionof the transaxle casing supporting the left axle on the distal leftwardside of the left differential side gear does not need expand leftward toincorporate the thrust collar and the shifter, thereby ensuring theminimized shape of the transaxle casing.

Preferably, the cylindrical part is formed integrally with the firstdifferential side gear. Therefore, the number of component parts isreduced so as to facilitate assembling the differential lockingmechanism.

Further preferably, the first differential side gear formed with thecylindrical part is made of steel, and the second differential side gearand the differential pinion are made of powder metal. Therefore, thecylindrical part made of steel has a sufficient strength for supportingthe differential locking slider thereon while keeping the powder metalas economic material for making the second differential side gear andthe differential pinion.

Alternatively, preferably, the cylindrical part is a member separatedfrom the first differential side gear. Therefore, a common differentialside gear can be used as either the first or second differential sidegear, thereby promoting standardization of component parts, and therebyreducing costs.

Further preferably, the cylindrical part is made of steel, and the firstand second differential side gears and the differential pinion are madeof powder metal. Therefore, only the cylindrical part is made of steelso as to ensure a sufficient strength for supporting the differentiallocking slider thereon, while the number of parts made of the economicpowder metal is increased so as to reduce costs.

These and other objects, features and advantages of the embodiments willappear more fully from the following detailed description of theinvention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, withreference to the accompanying drawings which are meant to be exemplary,not limiting, and wherein like elements are numbered alike in severalFigures, in which:

FIG. 1 is a perspective view of a transaxle.

FIG. 2 is a sectional plan view of the transaxle.

FIG. 3 is a sectional rear view of the transaxle showing a differentiallocking mechanism.

FIG. 4 is a sectional side view of the transaxle showing thedifferential locking mechanism.

FIG. 5 is a sectional side view of a differential side gear, acylindrical member, and a differential locking slider for an alternativedifferential locking mechanism.

FIG. 6 is a cross sectional view taken along VI-VI line of FIG. 5.

DETAILED DESCRIPTION

Referring to FIGS. 1 to 4, a general structure of a transaxle 1 will bedescribed. Transaxle 1 includes a transaxle casing 10. Transaxle casing10 includes an upper housing 11 and a lower housing 12 joined to eachother. Upper housing 11 is formed with a center portion 11 a, a rightaxle support portion 11 b extended rightward from center portion 11 a,and a left axle support portion 11 c extended leftward from centerportion 11 a. Lower housing 12 is joined at a horizontal top surfacethereof to a horizontal bottom surface of center portion 11 a of upperhousing 11 between right and left axle support portions 11 b and 11 c,and center portion 11 a of upper housing 11 and lower housing 12 arefastened together by bolts 13, thereby constituting transaxle casing 10.

Center portion 11 a of upper housing 11 and lower housing 12 joined toeach other form an HST chamber 10 a and a gear chamber 10 b therein. AnHST 3 is disposed in HST chamber 10 a. A reduction gear train 4 and adifferential gear unit 5 are disposed in gear chamber 10 b. Hereinafter,description will be based on an assumption that transaxle 1 is locatedso that a portion of gear chamber 10 b incorporating reduction geartrain 4 is extended along a left side of HST chamber 10 a and forwardfrom a rear portion of gear chamber 10 b incorporating differential gearunit 5.

Transaxle 1 carrying right and left axles 2R and 2L is configured sothat HST 3 receives power from the outside of transaxle 1 and outputsthe power to right and left axles 2R and 2L via reduction gear train 4and differential gear unit 5. Right axle 2R is extended through rightaxle support portion 11 b, and is journalled by a bearing (not shown) ina distal right end portion (not shown) of right axle support portion 11b. Left axle 2L is extended through left axle support portion 11 c, andis journalled by a bush (or needle bearing) 23 in a distal left endportion of left axle support portion 11 c. Proximal end portions ofrespective right and left axles 2R and 2L are disposed in the rearportion of gear chamber 10 b. More specifically, the proximal endportions of right and left axles 2R and 2L are fitted into an axialcenter hole 51 a of a later-discussed bull gear 51 of differential gearunit 5 so as to face each other in axial center hole 51 a. Right axle 2Ris extended rightward from a later-discussed gear assembly ofdifferential gear unit 5 so that right axle 2R is disposed rearward froma rear side of HST chamber 10 a, and is extend laterally along the rearside of HST chamber 10 a.

HST 3 includes a center section 31, an axial piston type hydraulic pump32 mounted on center section 31, and an axial piston type hydraulicmotor 33 mounted on center section 31. Center section 31 is extended ata right end thereof along a right side of HST chamber 10 a so as to haveits front end adjacent to a front side of HST chamber 10 a, and its rearend adjacent to the rear end of HST chamber 10 a. Center section 31 isformed at a rear half portion thereof with a horizontal surface, onwhich hydraulic pump 32 is mounted so as to extend upward from the rearhalf portion of center section 31. A vertical pump shaft 34 serving as arotary axis of hydraulic pump 32 (i.e., an input shaft of HST 3) isjournalled at a lower portion thereof in the rear half portion of centersection 31, and is extended upward so as to have a top portion thereofprojecting upward from a top of center portion 11 a of upper housing 11of transaxle casing 10. An input pulley 34 a and a cooling fan 34 b arefixed on the top portion of pump shaft 34, as shown in FIG. 1. Inputpulley 34 a is drivingly connected to a prime mover, e.g., an internalcombustion engine, via a belt (not shown) looped over input pulley 34 a.

Center section 31 is formed at a front half portion thereof with avertical surface, on which hydraulic motor 33 is mounted so as to extendleftward from the front half portion of center section 31. A lateralhorizontal motor shaft 35 serving as a rotary axis of hydraulic motor 33(i.e., an output shaft of HST 3) is journalled at a right portionthereof in the front half portion of center section 31, and is extendedleftward so as to have a left end portion thereof projecting into thefront portion of gear chamber 10 b through a partition wall formed intransaxle casing 10 to define the left side of HST chamber 10 a.

Center section 31 is formed therein with fluid passages (not shown)fluidly connecting hydraulic pump 32 to hydraulic motor 33. Hydraulicpump 32 includes a movable swash plate (not shown) for controlling anamount of fluid delivered from hydraulic pump 32 and a flow direction offluid delivered from hydraulic pump 32, thereby controlling rotationalspeed and direction of motor shaft 35 of hydraulic motor 33. A lateralhorizontal pump control shaft 36 is pivotally supported by a right sidewall of center portion 11 a of upper housing 11 of transaxle casing 10defining the right side of HST chamber 10 a. In HST chamber 10 a, aninner end of pump control shaft 36 is interlockingly connected to themovable swash plate. Outside of transaxle casing 10, an arm 36 a isfixed on an outer end of pump control shaft 36 so as to be operativelyconnected to a speed control manipulator (e.g., a lever or a pedal)provided in a vehicle, for instance.

In HST chamber 10 a, a neutral returning spring 37 is coiled around pumpcontrol shaft 36. A spring expansion arm 38 is fixed on pump controlshaft 36, and is extended along the right side of HST chamber 10 a. Apressure pin 38 a is extended laterally horizontally from springexpansion arm 38. A laterally horizontal spring retaining pin 39 issupported by the right side wall of center portion 11 a of upper housing11 forward from pump control shaft 36. In HST chamber 10 a, both ends ofneutral returning spring 37 are twisted to cross each other, and areextended so as to nip pressure pin 38 a and spring retaining pin 39therebetween at a rotational position of pump control shaft 36corresponding to a neutral position of the movable swash plate.

If pump control shaft 36 is rotated from the rotational positioncorresponding to the neutral position of the movable swash plate,pressure pin 38 a of spring expansion arm 38 rotates together with pumpcontrol shaft 36 so as to push one end portion of neutral returningspring 37 away from another end portion of neutral returning spring 37retained by spring retaining pin 39, thereby generating a spring forceof neutral returning spring 37 to bias pump control shaft 36 to therotational position corresponding to the neutral position of the movableswash plate. Incidentally, spring retaining pin 39 is an eccentric pinconfigured so that the rotational position of pump control shaft 36defined by pressure pin 38 a and spring retaining pin 39 nipped byneutral returning spring 37 can be adjusted by rotating spring retainingpin 39 so as to accurately match with the neutral position of themovable swash plate.

Reduction gear train 4 disposed in gear chamber 10 b includes a motoroutput gear 41, a counter shaft 42, a large diametric counter gear 43, asmall diametric counter gear 44, and bull gear 51 that also serves as aninput gear of differential gear unit 5. Motor output gear 41 is fixed onthe left end portion of motor shaft 35 in gear chamber 10 b. Countershaft 42 is extended laterally horizontally and is disposed in gearchamber 10 b between motor shaft 35 forward therefrom and differentialgear unit 5 rearward therefrom. Small diametric counter gear 44 isfitted on counter shaft 42 so as to extend along counter shaft 42between right and left sides of a fore-and-aft intermediate portion ofgear chamber 10 b, and meshes at a rear end thereof with bull gear 51.Large diametric counter gear 43 is fixed on small diametric counter gear44 and meshes at a front end thereof with motor output gear 41.Therefore, reduction gear train 4 is configured so as to transmit powerfrom motor shaft 35 to bull gear 51 of differential gear unit 5 viamotor output gear 41, large diametric counter gear 43 and smalldiametric counter gear 44.

Further, a spacer ring 45 is provided around small diametric countergear 44 between large diametric counter gear 43 and bull gear 51 so asto ensure a space rearward therefrom between large diametric countergear 43 and bull gear 51. A later-discussed differential lockingmechanism 6 includes a cylindrical part 61 and a differential lockingslider 62 axially slidably fitted on cylindrical part 61, which arepassed through the space rearward from spacer ring 45 between largediametric counter gear 43 and bull gear 51. Therefore, this space isused for arranging cylindrical part 61 and differential locking slider62 around a left differential side gear of differential gear unit 5serving as a later-discussed first differential side gear 53, therebybeing advantageous to constitute differential locking mechanism 6.

A brake 7 for braking motor shaft 35 is disposed in a front end portionof gear chamber 10 b. In this regard, motor output gear 41 is formedwith a flange serving as a brake disc 41 a. Brake 7 includes a verticalcamshaft 71, a brake shoe 72, and a brake pad 73. Camshaft 71 ispivotally supported by transaxle casing 10 and is formed with asectionally semicircular portion having a vertical cam surface 71 a ingear chamber 10 b. Cam surface 71 a faces brake shoe 72 disposed betweencamshaft 71 and a front end portion of brake disc 41 a. Brake pad 73 isfitted to a wall of transaxle casing 10 so that the front end portion ofbrake disc 41 a is disposed between bake shoe 72 and brake pad 73.Normally, camshaft 71 is rotationally located so as to extend camsurface 71 a parallel to brake shoe 72, thereby separating brake disc 41a from brake shoe 72 and bake pad 73 so as to keep rotation of motorshaft 35 freely from brake 7. When brake 7 is applied, camshaft 71 isrotated to locate cam surface 71 a slantwise relative to brake shoe 72so as to thrust brake shoe 72, whereby brake disc 41 a is pressedbetween brake shoe 72 and brake pad 73, thereby braking motor shaft 35and axles 2R and 2L drivingly connected to motor shaft 35 via reductiongear train 4 and differential gear unit 5.

Differential gear unit 5 and differential locking mechanism 6 will bedescribed with reference to FIGS. 2 to 4. Differential gear unit 5includes bull gear 51, differential pinions 52, a first differentialside gear 53, a second differential side gear 54, and right and leftaxles 2R and 2L. Differential locking mechanism 6 is defined asdifferential gear unit 5 plus a cylindrical part 61, a differentiallocking slider 62, a fork 63, a fork shaft 64, a spring 65, a stopperring 66, and a differential locking arm 67. In other words, differentiallocking mechanism 6 is configured so as to use these additional members61, 62, 63, 64, 65, 66 and 67 for locking right and left axles 2R and 2Ltogether so as to prevent right and left axles 2R and 2L fromdifferentially rotating.

Bull gear 51 serving as an input gear of differential gear unit 5 mesheswith small diametric counter gear 44 so as to also constitute reductiongear train 4. Bull gear 51 is bored through with lateral axial centerhole 51 a. As mentioned above, the axially proximal end portions ofright and left axles 2R and 2L (i.e., a left end portion of right axle2R and a right end portion of left axle 2L) are fitted into axial centerhole 51 a in bull gear 51 so as to face each other, so that right andleft axles 2R and 2L also serve as output shafts of differential gearunit 5. Therefore, when bull gear 51 is rotated by power from motorshaft 35 via reduction gear train 4, right and left axles 2R and 2Lrotate together with bull gear 51, however, right and left axles 2R and2L are allowed to rotate relative to each other and to bull gear 51.

Bull gear 51 is formed therein with a pair of pinion holes 51 bsymmetrically with respect to axial center hole 51 a. A pair of bevelpinions serving as differential pinions 52 are disposed in symmetricpinion holes 51 b, respectively. Each differential pinion 52 has a pivotshaft 52 a extended in a radial direction of bull gear 51. As a result,pivot shafts 52 a of respective differential pinions 52 are disposedcoaxially to each other with axial center hole 51 a therebetween, andsymmetric differential pinions 52 are pivoted in bull gear 51 viarespective pivot shafts 52 a.

A bevel gear serving as first differential side gear 53 is fixed on oneof axles 2R and 2L, and another bevel gear serving as seconddifferential side gear 54 is fixed on the other of axles 2R and 2L, sothat first and second differential side gears 53 and 54 adjoin bull gear51 therebetween. Therefore, each of differential pinions 52 meshes atright and left sides thereof with first and second differential sidegears 53 and 54. First differential side gear 53 is defined as a gearprovided with cylindrical part 61 for constituting differential lockingmechanism 6, while second differential side gear 54 is defined as a gearthat is not provided with cylindrical part 61. In this embodiment, firstdifferential side gear 53 is a left differential side gear fixed on leftaxle 2L adjacent to a left end surface of bull gear 51, and seconddifferential side gear 54 is a right differential side gear fixed onright axle 2R adjacent to a right end surface of bull gear 51.

Cylindrical part 61 includes a vertical plate portion 61 a at an axiallydistal end (in this embodiment, a left end) thereof joined to an axiallydistal end (in this embodiment, a left end) of first differential sidegear 53 so as to be provided on first differential side gear 53unrotatably relative to first differential side gear 53. Cylindricalpart 61 includes a circumferential portion 61 b extended in the axialdirection of axles 2L and 2R from an outer circumferential end ofvertical plate portion 61 a toward bull gear 51 so as to surround firstdifferential side gear 53. Differential locking slider 62 isspline-fitted on circumferential portion 61 b of cylindrical part 61unrotatably relative to cylindrical part 61 and slidably in the axialdirection parallel to axles 2L and 2R. Differential locking slider 62 isformed at an axial proximal end (in this embodiment, a right end)thereof with pawls 62 a as a typical form of a projection.

Bull gear 51 is formed therein with slots 51 c corresponding torespective pawls 61 a of differential locking slider 62. Slots 51 c area typical form of a recess for receiving the projection of differentiallocking slider 62. To ensure a proper function as differential lockingmechanism 6, slot 51 c may be open at only the left end surface of bullgear 51 facing differential locking slider 62, and may be closed at theright end surface of bull gear 51 opposite differential locking slider62. However, in this embodiment, slots 51 c are laterally extended topenetrate bull gear 51 so as to be also open at the right end surface ofbull gear 51 opposite differential locking slider 62. Slot 51 cpenetrating bull gear 51 is advantageous so that common bull gear 51 canbe used without reversing whether the right differential side gear orthe left differential side gear may serve as first differential sidegear 53 provided with cylindrical part 61 having differential lockingslider 62 fitted thereon.

Differential locking slider 62 is slidable in a differential lockingdirection (in this embodiment, rightward) toward bull gear 51 so as toinsert pawls 62 a into respective slots 51 c in bull gear 51, and in adifferential unlocking direction (in this embodiment, leftward) awayfrom bull gear 51 so as to remove pawls 62 a from respective slots 51 c.

Alternatively, bull gear 51 may include a projection such as pawls, anddifferential locking slider 62 may include a recess for receiving theprojection, such as slots. The only requirement for bull gear 51 anddifferential locking slider 62 is that bull gear 51 and differentiallocking slider 62 include respective engagement parts, and differentiallocking slider 62 is slidable in one (in the present embodiment,rightward) axial direction of axles 2R and 2L so as to engage itsengagement part with the engagement part of bull gear 51, and in another(in the present embodiment, leftward) axial direction of axles 2R and 2Lso as to disengage its engagement part from the engagement part of bullgear 51.

Differential locking slider 62 is formed with an annular fork groove 62b into which fork 63 is fitted. Fork 63 is formed with a boss 63 a,which is fitted on fork shaft 64 rotatably relative to fork shaft 64 andaxially slidably along fork shaft 64. Fork shaft 64 is extendedlaterally horizontally (parallel to axles 2R and 2L) and is pivotallysupported by a rear lower portion of lower housing 12 unmovably in theaxial direction. In this regard, lower housing 12 is formed with rightand left vertical walls 12 a and 12 b defined as right and left sides ofthe rear portion of gear chamber 10 b incorporating differential gearunit 5. Fork shaft 64 is journalled by right and left vertical walls 12a and 12 b of lower housing 12. The distal left end of cylindrical part61 joined to first differential side gear 53 serving as the leftdifferential side gear, and fork 63 are extended along left verticalwall 12 b of lower housing 12. Stopper ring 66 is provided on fork shaft64 between boss 63 a of fork 63 and right vertical wall 12 a of lowerhousing 12. Spring 65 is wound around fork shaft 64 and stopper ring 66,and is interposed between boss 63 a of fork 63 and right vertical wall12 a of lower housing 12 along which a distal right end of seconddifferential side gear 54 serving as the right differential side gear isdisposed.

In gear chamber 10 b, a pressure pin 64 a projects radially from forkshaft 64. Boss 63 a of fork 63 is formed with a cam groove 63 b having aleftwardly open V-shaped edge. One axial (in this embodiment, left) endportion of fork shaft 64 projects outward from right or left verticalwall 12 a or 12 b (in this embodiment, left vertical wall 12 b) so as tobe fixedly provided thereon with differential locking arm 67.Differential locking arm 67 is operatively connected to a differentiallocking manipulator (e.g., a lever or a pedal) in a vehicle, forinstance.

Normally, differential locking arm 67 and fork shaft 64 are rotationallylocated so that pressure pin 64 a is disposed in cam groove 63 b. Spring65 biases fork 63 leftward so that pressure pin 64 a is fitted to adeepest end of cam groove 63 b, thereby locating differential lockingslider 62 at a differential unlocking position as a limit position ofthe leftward slide thereof in the differential unlocking direction,where pawls 62 a are removed from respective slots 51 c. Therefore, bullgear 51 is free from differential locking slider 62 so as to allow leftaxle 2L with first differential side gear 53 fixed thereon to rotaterelative to bull gear 51 and right axle 2R with second differential sidegear 54 fixed thereon.

When the differential locking manipulator is operated for differentiallocking of axles 2R and 2L, differential locking arm 67 and fork shaft64 are rotated so that pressure pin 64 a is rotated circumferentially offork shaft 64 while spring 65 presses the leftwardly open V-shaped edgeof cam groove 63 b against pressure pin 65 a. During the rotation offork shaft 64, fork shaft 64 is unmovable in the axial directionthereof. Therefore, as fork shaft 64 rotates together with pressure pin64 a, pressure pin 64 a moves along the edge of cam groove 63 b from thedeepest end of cam groove 63 b to a shallower portion of cam groove 63b, thereby thrusting boss 63 a of fork 63 rightward against spring 65.Accordingly, fork 63 moves rightward together with differential lockingslider 62, so that differential locking slider 62 is slid alongcircumferential portion 61 b of cylindrical part 61 in the differentiallocking direction to bull gear 51. Finally, boss 63 a comes to abutagainst stopper ring 66 so that differential locking slider 62 reaches adifferential locking position as a limit position of the rightward slidethereof in the differential locking direction, where pawls 62 a areinserted into respective slots 51 c. Therefore, bull gear 51 is lockedwith first differential side gear 53 fixed on left axle 2L, so thatsecond differential side gear 54 fixed on right axle 2R is also lockedwith first differential side gear 53 via differential pinions 52,thereby locking axles 2R and 2L to each other so as to prevent axles 2Rand 2L from rotating differentially.

The significant advantage of differential locking mechanism 6 is theminimization of the rear portion of gear chamber 10 b incorporatingdifferential locking mechanism 6 including differential gear unit 5 inthe axial direction of axles 2R and 2L. In this regard, an insidesurface of right vertical wall 12 a of lower housing 12 adjacent to thedistal right end of second differential side gear 54 provided with nocylindrical part 61 is spaced from the right end surface of bull gear 51by only an axial length of second differential side gear 54 from theproximal left end thereof to the distal right end thereof. Firstdifferential side gear 53, even provided with cylindrical part 61 havingdifferential locking slider 62 fitted thereon, has an axial length fromits proximal right end to its distal left end, which is equal to theaxial length of second differential side gear 54 provided with nocylindrical part 61, because cylindrical part 61 is joined at only itsdistal left end to the distal left end of first differential side gear53 so as to need no additional space on the distal leftward side of thedistal left end of first differential side gear 53. As a result, aninside surface of left vertical wall 12 b of lower housing 12 isadjoined to the distal left end of first differential side gear 53 so asto be spaced from the left end surface of bull gear 51 as much as seconddifferential side gear 54 spaced from the right end surface of bull gear51. Therefore, transaxle casing 10 does not have to be modified toexpand the rear portion of gear chamber 10 b leftward along left axle 2Lso as to accommodate differential locking mechanism 6 includingdifferential gear unit 5.

Similar to right and left vertical walls 12 a and 12 b of lower housing12, right and left sides 11 a 2 and 11 a 3 of an upward convex left rearportion 11 a 1 of center portion 11 a of upper housing 11 defining rightand left sides of an upper half of the rear portion of gear chamber 10 bincorporating an upper half of differential locking mechanism 6including differential gear unit 5 are disposed adjacent to the axiallydistal ends of respective first and second differential side gears 53and 54, and are formed in vertical thin plate-like shapes. Therefore,vertical thin plate-shaped right side 11 a 2 is square with a right rearportion 11 a 4 of center portion 11 a of upper housing 11, which isextended rightward from a bottom portion of right side 11 a 2 to supportright axle 2R. Also, vertical thin plate-shaped left side 11 a 3 issquare with left axle support portion 11 c of upper housing 11 extendedleftward from a bottom portion of left side 11 a 3.

Incidentally, to journal proximal portions of axles 2R and 2L intransaxle casing 10, a bush 21 is fitted on right axle 2R on the distalrightward side of second differential side gear 54, and a bush 22 isfitted on left axle 2L on the distal leftward side of first differentialside gear 53. Bushes 21 and 22 are fitted at lower halves thereof inlower semicircular recesses formed on top portions of respective rightand left vertical walls 12 a and 12 b, and are fitted at upper halvesthereof in upper semicircular recesses formed on the bottom portions ofrespective right and left sides 11 a 2 and 11 a 3, whereby axles 2R and2L are clamped between upper and lower housings 11 and 12 via bushes 21and 22. However, bushes 21 and 22 are radially narrow so as not toseriously expand portions of transaxle casing 10 therearound. Therefore,the square corners between right side 11 a 2 of left rear portion 11 a 1of center portion 11 a and right rear portion 11 a 4 of center portion11 a and between left side 11 a 3 of left rear portion 11 a 1 of centerportion 11 a and left axle support portion 11 c are kept from beingbroken by expansion of the bottom portions of right and left sides 11 a2 and 11 a 3 accommodating the upper halves of bushes 21 and 22.

Especially, the square corner between right side 11 a 2 of left rearportion 11 a 1 of center portion 11 a and right rear portion 11 a 4 ofcenter portion 11 a is advantageous for mounting a rectangular fluidreservoir 25 on right rear portion 11 a 4 of center portion 11 a ofupper housing 11. Right rear portion 11 a 4 of center portion 11 a ofupper housing 11 is vertically thin because it only surrounds right axle2R, and extended laterally along right axle 2R continuously to rightaxle support portion 11 b. Further, as mentioned above, the rear side ofHST chamber 10 a disposed at a front end of right rear portion 11 a 4 ofcenter portion 11 a supporting right axle 2R is extended laterally alongright axle 2R. The rear side of HST chamber 10 a is square with rightrear portion 11 a 4 of center portion 11 a similarly to right side 11 a2 of left rear portion 11 a 1 of center portion 11 a. Therefore,rectangular fluid reservoir 25 for reserving fluid used as hydraulicfluid for HST 3 and as lubricating fluid for transaxle 1 is mounted onright rear portion 11 a 4 of center portion 11 a (and right axle supportportion 11 b) of upper housing 11 of transaxle casing 10 so as to beadjacent at a left end thereof to right side 11 a 2 of left rear portion11 a 1 of center portion 11 a of upper housing 11, and so as to beadjacent at a front end thereof to a wall portion of center portion 11 aof upper housing 11 defining the rear side of HST chamber 10 a.

Upwardly convex left rear portion 11 a 1 of center portion 11 a of upperhousing 11 is formed with an upwardly open port 11 a 5 above the rearportion of gear chamber 10 b therein incorporating differential lockingmechanism 6 including differential gear unit 5. An orifice 25 a isextended leftward from fluid reservoir 25 mounted rightward from leftrear portion 11 a 1 of center portion 11 a, and is bent downward so asto be fitted into port 11 a 5. Orifice 25 a serves as a siphon in fluidreservoir 25. Therefore, fluid is siphoned from fluid reservoir 25 intogear chamber 10 b via orifice 25 a so as to be supplied as lubricatingfluid for gears and other members in gear chamber 10 b.

Further, fluid reservoir 25 is provided on a rightward top portionthereof (laterally opposite orifice 25 a) with a fluid-feeding holecovered with a cap 25 b. Fluid reservoir 25 is provided with a breatherhole 25 c adjacent to the fluid-feeding hole, however, at a positionwhere fluid fed into fluid reservoir 25 via the fluid-feeding hole isprevented from leaking via breather hole 25 c. In this regard, an outerwall of fluid reservoir 25 is formed with a vertical portion extendedupward from a bottom portion thereof so as to define a vertical recess25 d open at the bottom portion of fluid reservoir 25 to the atmosphere.A top portion of the outer wall of fluid reservoir 25 defining verticalrecess 25 d is disposed immediately under the top portion of fluidreservoir 25, and is provided with breather hole 25 c communicating aninside space of fluid reservoir 25 to an outside space of fluidreservoir 25 in recess 25 d. Therefore, air is breathed out frombreather hole 25 c to the atmosphere via the space in vertical recess 25d.

As mentioned above, first differential side gear 53 provided withcylindrical part 61 is equal in the axial length thereof to seconddifferential side gear 54 provided with no cylindrical part 61, so thatthe rightward space in the rear portion of gear chamber 10 b from theright end surface of bull gear 51 to right side 11 a 2 of upper housing11 and right vertical wall 12 a of lower housing 12 is equal in volumeto the leftward space in the rear portion of gear chamber 10 b from theleft end surface of bull gear 51 to left side 11 a 3 of upper housing 11and left vertical wall 12 b, except that a front right portion of therear portion of gear chamber 10 b incorporating differential gear unit 5is narrowed by a left rear corner of HST chamber 10 a. Therefore, theright differential side gear fixed on right axle 2R may serve as firstdifferential side gear 53 provided with cylindrical part 61 withoutrequiring axially rightward expansion of the rear portion of gearchamber 10 b (narrowing the space for mounting fluid reservoir 25 onright rear portion 11 a 4 of upper housing 11), except that is should beconsidered the right front portion of the rear portion of gear chamber10 b needs to be expanded to ensure a space for arranging front portionsof cylindrical part 61 and differential locking slider 62.

In the above-mentioned embodiment shown in FIGS. 2 to 4, cylindricalpart 61 is joined at the distal end thereof to the distal end of firstdifferential side gear 53 because cylindrical part 61 is formedintegrally with first differential side gear 53. In other words, thedistal end portion of first differential side gear 53 is extendedcentrifugally so as to form vertical plate portion 61 a of cylindricalpart 61, and is bent rightward to extend toward bull gear 51 so as toform circumferential portion 61 b of cylindrical part 61. Therefore,first differential side gear 53 and cylindrical part 61 are made of thesame material. Since differential locking slider 62 is spline-fitted oncircumferential portion 61 b of cylindrical part 61, first differentialside gear 53 and cylindrical part 61 are made of steel to ensure astrength of cylindrical part 61 supporting differential locking slider62. On the other hand, second differential side gear 54 and symmetricdifferential pinions 52 are made of powder metal for reducing costs.

Referring to FIGS. 5 and 6, in an alternative embodiment, cylindricalpart 61 is a member separated from first differential side gear 53.Vertical plate portion 61 a of cylindrical part 61 is formed at an innercircumferential edge thereof with notches in correspondence to the shapeof gear teeth of the distal end portion of first differential side gear53. To join the axial distal end portion of cylindrical part 61 to theaxially distal end portion of first differential side gear 53, the gearteeth of first differential side gear 53 are fitted at the axiallydistal end thereof to the respective notches on the innercircumferential edge of vertical plate portion 61 a of cylindrical part61, thereby making cylindrical part 61 unrotatable relative to firstdifferential side gear 53. To surely fix cylindrical part 61 to firstdifferential side gear 53, the inner circumferential edge of verticalplate portion 61 a of cylindrical part 61 may be joined to the axiallydistal end portion of first differential side gear 53 by welding or byadditional fastening member, e.g., a pin or a bolt.

In the embodiment of FIGS. 5 and 6, only cylindrical part 61 is made ofsteel to ensure the required strength of circumferential portion 61 bfor supporting differential locking slider 62 fitted thereon. Firstdifferential side gear 53 can be a gear identical to second differentialside gear 54. In other words, a common gear formed as a differentialside gear can be used as either first differential side gear 53, ifcylindrical part 61 is fixed thereon, or second differential side gear54, if it is not provided with cylindrical part 61. Therefore, thecommon differential side gear is made of economic powder metal forproviding both first and second differential side gears 53 and 54 madeof powder metal. Similarly, a common gear formed as a differentialpinion is made of economic powder metal for providing both symmetricdifferential pinions 52 made of powder metal.

It is further understood by those skilled in the art that the foregoingdescription is given to preferred embodiments of the disclosed apparatusand that various changes and modifications may be made in the inventionwithout departing from the scope thereof defined by the followingclaims.

While the description above refers to particular embodiments of thepresent invention, it will be understood that many modifications may bemade without departing from the spirit thereof. The accompanying claimsare intended to cover such modifications as would fall within the truescope and spirit of the present invention.

The presently disclosed embodiments are therefore to be considered inall respects as illustrative and not restrictive, the scope of theinvention being indicated by the appended claims, rather than theforegoing description, and all changes which come within the meaning andrange of equivalency of the claims are therefore intended to be embracedtherein.

What is claimed is:
 1. A differential locking mechanism comprising:first and second axles extended coaxially to each other; a firstdifferential side gear fixed on the first axle; a second differentialside gear fixed on the second axle; a bull gear disposed between thefirst and second side gears, the bull gear including an axial centerhole and an engagement part radially outward from the axial center hole,wherein axial proximal ends of the first and second axles are fitted inthe axial center hole so as to face each other so that the first andsecond axles are rotatable relative to each other and to the bull gear;a differential pinion pivoted in the bull gear and meshing at oppositesides thereof with the first and second differential side gears; acylindrical part provided on the first differential side gearunrotatably relative to the first differential side gear, thecylindrical part including a circumferential portion surrounding thefirst differential side gear; and a differential locking slider fittedon the circumferential portion of the cylindrical part unrotatablyrelative to the cylindrical part, the differential locking sliderincluding an engagement part, wherein the differential locking slider isslidable along the circumferential portion of the cylindrical part inone axial direction of the first and second axles so as to engage theengagement part of the differential locking slider with the engagementpart of the bull gear, and in another axial direction of the first andsecond axles so as to disengage the engagement part of the differentiallocking slider from the engagement part of the bull gear.
 2. Thedifferential locking mechanism according to claim 1, wherein thecylindrical part is formed integrally with the first differential sidegear.
 3. The differential locking mechanism according to claim 2,wherein the first differential side gear formed with the cylindricalpart is made of steel, and wherein the second differential side gear andthe differential pinion are made of powder metal.
 4. The differentiallocking mechanism according to claim 1, wherein the cylindrical part isa member separated from the first differential side gear.
 5. Thedifferential locking mechanism according to claim 4, wherein thecylindrical part is made of steel, and wherein the first and seconddifferential side gears and the differential pinion are made of powdermetal.